[Haskell-beginners] How to display a time difference?

[Colin Paul Adams]

>>>>> "Yitzchak" == Yitzchak Gale <gale at sefer.org> writes:

    Yitzchak> Colin Paul Adams wrote:
    >> The code of the following routine is intended to indicate how
    >> long it takes for the computer to make a move. However the time
    >> is printed (as very close to zero) long before the move is
    >> made.

    Yitzchak> You are writing a thunk to the IORef. It only gets
    Yitzchak> computed later on when you read the value.

    Yitzchak> Try using:

    >> readIORef game_state_ior >>= evaluate
    >> . update_interactive_from_move move >>= writeIORef
    >> game_state_ior

    Yitzchak> evaluate is in Control.Exception.

Still no joy with:

play_move :: IORef Game_state -> IO ()
play_move game_state_ior = do
  (_, state, _) <- readIORef game_state_ior  
  putStr "Playing AI: "
  start_time <- getCurrentTime
  let move = recommended_move state
  readIORef game_state_ior >>=
    evaluate . update_interactive_from_move move >>=
             writeIORef game_state_ior
  end_time <- getCurrentTime
  putStrLn $ show $ (diffUTCTime end_time start_time)


-- 
Colin Adams
Preston Lancashire